John F. Kennedy Jr. could have taken several crucial precautions that would have made his flight to Martha’s Vineyard safer, experts said yesterday.

Kennedy took off from Essex County Airport in Fairfield, N.J., without filing a flight plan – which would have given rescuers his route, his estimated time of arrival and the number of people on board.

“Without a flight plan, you’re flying blind,” said Dr. Clifford Bragdon, director of the National Aviation and Transportation Center at Long Island’s Dowling College.

“No one has any way of knowing where you are.”

Kennedy was not required to file the plan since he was flying under “visual flight rules” – meaning the pilot has to count on his seeing other planes and their seeing him – but cautious pilots generally do, Bragdon said.

“It not a question of legality – it’s a question of prudence,” Bragdon said.

Kennedy was already pushing the envelope by simply making the flight, which left New Jersey about 8:38 p.m.

The amateur flier – who had logged fewer than 100 flight hours as a licensed pilot – took off in his single-engine Piper Saratoga II HP at night and into hazy skies with only 4 to 5 miles of visibility.

The minimum legal visibility for VFR flight is 3 miles. Anything less than six miles is considered marginal – but still legal.

“It was hazy black. You really couldn’t make out what was up and what was down,” said NBC correspondent Dr. Bob Arnot, who flew the route about the same time as Kennedy.

Kennedy had earned his pilot’s license in May 1998 but did not have the higher-grade instrument rating, which could have helped him better navigate the unfavorable conditions, experts said.

“This flight was not prudent,” Jim Burnett, a former chairman of the National Transportation Safety Board, told MSNBC.

Kennedy also did not keep in touch with air traffic controllers along his route – another optional but sensible move, according to Col. Steve Roark, of the U.S. Air Force.

If he had filed a flight plan and talked to air controllers, authorities would have known the plane was missing almost immediately after the apparent accident, Bragdon said.

The Federal Aviation Administration reported a radar blip from the plane was recorded at 9:39 p.m. off the southwest coast of Martha’s Vineyard. But the search did not begin until concerned family members notified authorities at 2:15 a.m.

Without a flight plan or tower contact, authorities had to pour over radar tapes – looking for unidentified blips that could have been Kennedy’s plane.

The plane’s electronic locator transmitter – also called a “beacon” – is supposed to send a radio distress signal on impact.

But the signal does not generally work in water, said Margaret Napolitan, director of air safety for The New Piper Aircraft, Inc., the plane’s manufacturer.

Kennedy bought the powerful six-seater in April from a pilot who had owned it since 1995, Napolitan said.

It’s considered a very fast and powerful aircraft for a new pilot to fly.

The plane – powerful enough to carry a grand piano – can fly up to 15,588 feet, cruises at 163 knots and can fly 740 nautical miles on a tank of gas.